Conditional access systems, such as satellite, cable television, and direct subscriber line (DSL) systems, often encrypt services that subsequently must be decrypted with encrypting keys prior to viewing. Encryption devices encrypt these services using a series of keys that change on a regular basis to ensure protection of the content. The time interval during which a single key is used is called a cryptoperiod. For example, an encrypting key may change every four (4) seconds; therefore, a cryptoperiod including a changed encrypting key is transmitted every 4 seconds from each encryption device for each encrypted service.
Decoder devices, such as set top boxes, receive the services along with periodic encryption messages, which require timely processing in order to decrypt the received services. Importantly, messages containing the encrypting keys (often embedded within Entitlement Control Messages called ECMs) received by a set top box or other host device are important elements for proper functioning in a conditional access system. Namely, ECMs must be processed within the given time window, for example, every 4 seconds, in order to avoid service interruptions, such as video or audio artifacts. Note that different conditional access technologies use various means for transmission of service encryption keys, which may be included within ECMs and/or other messages, but for the purposes of this application, the term ECMs is meant to include all messages sent in conjunction with, and associated with changes to, the service encryption key.
Often, ECMs are processed by a CAS client on a secure microprocessor device within the set top box or other host device. The secure microprocessor is often single threaded with limited input/output (I/O) bandwidth, and yet must be able to handle the processing load for ECMs of multiple services. As a result, if the number of services requiring decryption increases, the processing demand on the secure microprocessor will also increase, and the chance that multiple ECMs will require simultaneous processing also increases. If this ECM processing demand is not met, especially the demand for processing of multiple simultaneous ECMs, there is a risk of service interruptions. Additionally, it is extremely prohibitive to upgrade the capabilities of the secure microprocessor after it is deployed. Thus, there exists a need for a more efficient system and method that eliminates or at least limits cases where ECMs, or other real-time messages in the encryption system required for decryption of services, from multiple services would need to be processed simultaneously.